Field of the Invention
The present invention relates to an optical receiver and a detection method.
Related Background of the Invention
Multi-Source Agreement (MSA) defines the standards about an external shape, pin assignment, electrical characteristics, and optical characteristics, and so on of an optical transceiver. Most of the MSAs require also a functionality of digital diagnostic monitoring (DDM) to monitor/diagnose a state of optical communication and an internal operation state of the optical transceiver in real time and notifies an external device (upper layer) of a diagnosis result through a predetermined digital communication interface. The information on the state of the optical communication notified by the DDM includes, for instance, received signal intensity of an optical signal input to the optical transceiver as a part thereof. A monitor circuit of a prior art monitors the received signal intensity under a restricted frequency bandwidth, so that a monitor value is acquired with necessary measurement precision by suppressing an influence of noise (for example, JP-A-62-235834).
Meanwhile, recently, development of an optical transceiver such as 100G form-factor pluggable (CFP) has progressed and realized downsizing and low power consumption for a high speed and a large capacity of a communication network. In an optical receiving unit of the CFP, a multiplexed optical signal comprising four optical signals with different wavelengths from each other is separated by an optical demultiplexer, and the received signal intensity is measured for each of the four optical signals separated by the optical multiplexer. Here, if the conventional technology is applied to the four optical signals as it is, a total size of the respective measurement circuits and number of wiring lines interconnecting each of the measurement circuits with other may increase fourfold and thus, the conventional technology is not preferable from the viewpoint of downsizing.
As an approach to solve the problem, one may consider configuring one monitor circuit to measure received signal intensity by sequentially switching the four optical signals one by one and measuring the respective received signal intensitys in a time division method. However, a large capacitance of a capacitor provided in the monitor circuit is needed to improve measurement precision by restricting a the frequency band of the monitor circuit. Such a monitor circuit with a restricted frequency band may cause a rising edge and a falling edge of an output waveform of the monitor circuit to become blunt. When received signals are continuously measured in a short period, amplitude of the output waveform corresponding to the received signal intensity may not be acquired with required measurement precision. In this case, it is necessary to increase a switching period to measure the continuous received signals. As a result, a measurement time of the received signal intensity increases and a measurement result may not be transmitted to an upper layer in a time defined by the MSA or the frequency of measuring the received signal intensity per unit time may decrease.
The present invention has been made to solve the above-described problems and an object of the present invention is to provide a optical receiver and a detection method that can decrease a measurement time while securing measurement precision, in measurement of received signal intensity.